Liver transplantation is the only curative treatment for end stage liver disease. However, as with virtually any organ or tissue transplant, most recipients require lifetime immunosuppression; this carries with it a significant burden of associated costs as well as on-target and off-target side effects. Our long-term goal is to develop novel approaches that will facilitate reduction, and potentially elimination, of immunosuppressive drugs. Based on numerous animal and clinical studies, our working model is that long-term drug free allograft acceptance requires a combination of deletion of a large fraction of alloreactive cells and development/delivery of regulatory cells capable of inhibiting the specific immune response to the graft. Within this framework, our focus is the development of donor-specific regulatory T cells (Tregs) as a cellular therapeutic that can be used in conjunction with immunosuppressive drugs that either spare Tregs (e.g., mTOR or PI3K inhibitors) or that facilitate Treg expansion (e.g., low dose IL-2). Over the past several years we have developed methodology to expand and purify donor-specific Foxp3+ Tregs ex-vivo using costimulatory blockade (belatacept). To our knowledge, no other group is using this process to generate and isolate donor-specific Tregs. Moreover, we have just received an IND from the FDA for a phase I safety trial of Tregs made in this manner in live-donor renal allograft recipients. While this is an excellent setting for a safety study, we believe that the most immediate therapeutic potential for the use donor- specific Tregs to achieve immunosuppression reduction/withdrawal is in liver transplantation. To this end, the goal of the present application is to finalize the planning for a proposed clinical trial of donor-specific Tres in adult deceased donor liver transplantation. The objective(s) of the trial itself will be to (1): Perform an open label single center phase I/II dose escalation study pilot study in 9-15 hepatitis C virus negative recipients of deceased donor liver transplants, and (2): Conduct detailed immunological monitoring of the Treg recipients. Funds from the current R34 application will be used to complete the clinical trial protocol, finalize elements that may require adaptation in moving the Treg manufacturing process to the deceased donor liver transplant setting, finish design of the mechanistic studies, obtain the requisite IND amendment for the liver transplant trial, and establish the framework for trial operation and management. At the conclusion of the R34, we expect to have a final protocol, and to have submitted both an IND amendment and a final application for IRB approval for the clinical trial.